DESCRIPTION (from the application): Mitochondria DNA damage and mutations have been hypothesized to contribute to aging. This hypothesis is rounded on data demonstrating a correlation between increased age, increased mtDNA damage and mutations and decreased mitochondrial function. Mitochondria utilize 90% of cellular oxygen and generate reactive oxygen species that are capable of inflicting DNA damage. Because mtDNA is physically located near the sites of reactive oxygen species production, mtDNA sustains higher spontaneous levels of oxidative damage than nuclear DNA. While nuclear DNA is associated with histones, which may provide some protection from DNA damaging agents, mtDNA lacks histones. Mitochondria have evolved with DNA repair activities that can restore the integrity of DNA to a certain extent. However, mtDNA repair is more limited in scope than nuclear DNA repair. Together, these factors may contribute to an accumulation of mtDNA damage and mutations over time. However, a direct demonstration of mtDNA damage leading to mitochondrial dysfunction has not been reported. Contained within this proposal is a method to test the relationship between mtDNA damage and mitochondrial dysfunction. Levels of spontaneous oxidative DNA damage and mutations are partially determined by the ability of DNA repair mechanisms to ameliorate the damage that occurs in DNA. It is now possible to manipulate mtDNA repair and thereby test whether oxidative damage in mtDNA leads to dysfunction. Experiments are proposed in this application to determine if mitochondrial oxidative DNA damage contributes to mitochondrial dysfunction in older animals. The overall hypothesis to be tested in this proposal is that decreased mtDNA integrity results in mitochondrial dysfunction that contributes to aging.